Process for the prevention of cold flow in polybutadiene



United States Patent Ofitice 3,350,380 PROCESS FOR THE PREVENTION OF COLD FLOW IN POLYBUTADIENE Charles W. Strobe], Borger, Tex., assignor to Phillips Petroleum Company, a corporation of Delaware No Drawing. Original application Aug. 23, 1962, Ser. No. 218,853, now Patent No. 3,236,821, dated Feb. 22, 1966. Divided and this application Feb. 15, 1965, Ser. No. 432,808

9 Claims. (Cl. 26094.7)

This is a division of application Ser. No. 218,853, filed Aug. 23, 1962, now U.S. 3,236,821.

This invention relates to a method for preventing or to cold flow.

In recent years a great deal of research Work has been directed toward the production improved rubbery polymers. One of the has attracted Widein the processing of the polymers, particularly in packaging, shipping and storage, a certain amount of difi'iculty as b group consisting catalyst including an organo- 3,350,380 Patented Oct. 31, 1967 ture an organometal having the formula from cordance with the present invention.

The sulfur dioxide can be added to the material by itself.

In accordance with the above-described embodiment of the invention, the treating agents are added to the polymstopping of the reaction. When utilizing only sulfur dioxthe cis-poly-butadiene polymminutes to 50 hours.

Examples of specific R M compounds suitable for use include:

trimethylaluminum triisobutylaluminum tridodecylaluminum 3 trieicosylaluminum tricyclohexylaluminum tri(4-methylcyclohexyl) aluminum tribenzylaluminum triphenylaluminum tri( 2-naphthyl) aluminum n-propyldiphenylaluminum diethyl-n-hexylaluminum di-n-butylmercury methyleicosylmercury diethylzinc diphcnylzinc ethylcyclopentylzinc di( 3-isopropylcyclohexyl) beryllium dibutylberyllium diethylcadmium diisopropylcadmium diphenylmagnesium di-n-propylmagnesium dimethylmagnesium methylethylmagnesium tetraethyllead trimethylphenyllead triethyl gallium tri-n-hexylindium triisopropylthallium n-pentylsodium phenylsodium n-butylpotassium phenylpotassium and the like.

As discussed hereinbefore, the treating agents of this invention, i.e., oxygen or sulfur dioxide and, in the case of the org-anolithium-catalyzed polymerization, the R M compound, are added to the polymerization reaction mixture prior to the inactivation of the catalyst. In another embodiment of the invention, the polybutadiene recovered from the polymerization after quenching or shortstopping of the polymerization reaction is treated with the treating agents of this invention in order to reduce the tendency of the polymers to cold flow. In accordance with this embodiment, a cis-polybutadiene or an organolithiumcatalyzed polybutadiene is treated with oxygen or sulfur dioxide and a compound having the formula R M, wherein R, M and n are as defined hereinbefore. It is to be understood that in treating the polybutadiene product both the oxygen or sulfur dioxide and the R M compound are utilized. These materials can be added to the polybutadiene in any of the forms discussed hereinbefore, i.e., in the case of the sulfur dioxide or oxygen in the form of a gas, liquid or solution and in the case of the organometal as a solution or per se. It was completely unexpected when it was found that this combination of materials is effective in reducing cold flow since either of the materials is ineffective when used alone. While this embodiment of the invention is not dependent upon any particular reaction mechanism, it is important that both ingredients of the treating composition be intimately blended with the polybutadiene and that the time and temperautre of the treatment be adjusted to produce the desired effect.

Any suitable method for incorporating the treating agents into the polybutadiene product which will give an intimate blend of the treating agents with the rubber can be utilized. A convenient procedure is to blend a solution of the R M compound with a solution of the polymer and thereafter introduce the sulfur dioxide or oxygen in the form of a gas. The mixture is then agitated during the treating period. The treating temperature can vary over a rather broad range, e.g., from 50 to 250 F. It is usually preferred to operate at a temperature above 75 F. The time of treatment is dependent upon the temperature, longer periods being required for lower temperatures. However, the time of treatment is generally in the range of 5 minutes to 50 hours.

' of polybutadiene. When employing both of In one method of operation, the cis-polybutadiene or the organo-lithium-catalyzed polybutadiene is recovered from the reaction mixture in which it was prepared and dissolved in a hydrocarbon solvent or other material which is inert with respect to the treating agents. The polymer is then in condition for treatment as herein described. An alternative procedure is to quench the polymerization reaction mixture with a small amount of water after which excess water is removed with a suitable drying agent, such as anhydrous calcium sulfate. The resulting essentially anhydrous polymer solution is then treated with the treating agents. When operating in this manner, the steps of recovering and redissolving the polymer are eliminated. Another method for effecting the treatment of the polymer is to incorporate the treating agents into the rubbery polymer in a Banbury mixer or similar kneading device. When using this method of operation, the R M compound and polymer can be added to the mixer after which the mixing is carried out in an atmosphere of sulfur dioxide, oxygen or air. It is to be understood that in accordance with this embodiment of the invention the treating agents are employed with polymers in which no active polymerization catalyst is present. When treatment of the polymer is conducted in solution, the polymer can be recovered by any conventional means. For example, the polymer can be coagulated with a suitable reagent, such as an alcohol, or the solvent can be removed by steam stripping.

The amount of the sulfur dioxide or oxygen used in the practice of the present invention can vary over a relatively wide range, e.g., from 1 to 60, preferably from 1 to 25, millimols per 100 grams of polybutadiene. When the R M compound is employed, the amount used is generally in the range of 0.5 to 25 millimols per 100 grams the treating agents, an excess of the sulfur dioxide or oxygen is usually used. Generally, from 1.1 to 25 millirnols of sulfur dioxide or oxygen per millimol of R M compound is employed.

The treating agents of this invention are applicable to polybutadienes containing a high percentage of cis 1,4- addition and to the process for preparing such products. The cis-polybutadiene can be prepared by polymerizing butadiene with a catalyst systemwhich includes an organometal compound and iodine, present either in the free or combined state. This polymerization system produces a cis-polybutadiene having outstanding properties when in the cured state but having a tendency to cold flow in the unvulcanized state. The term cis-polybutadiene as used herein is intended to include a polybutadiene containing at least percent cis 1,4-addition, e.g., from 85 to 98 percent and higher.

The cis-polybutadienes can be prepared by polymerizing l,3-butadiene with any one of a large number of different stereospecific catalyst systems. It is usually preferred to employ a catalyst which is selected from the group consisting of (l) a catalyst comprising an organometal compound having the formula R M, wherein R is an alkyl, cycloalkyl, aryl, alkaryl, aralkyl, alkylcycloalkyl, cycloalkylalkyl, arylcycloalkyl or cycloalkylaryl radical, M is aluminum, mercury, zinc, beryllium, cadmium, magnesium, sodium or potassium, and m is equal to the valence of the metal M, and titanium tetraiodide, (2) a catalyst comprising an organometal compound having the formula R M, wherein R is an organo radical as defined above, M is aluminum, magnesium, lead, sodium or potassium, and n is equal to the valence of the metal M, titanium tetrachloride and titanium tetraiodide, (3) a catalyst comprising an organometal compound having the formula R M, wherein R is an organo radical as defined above, M is aluminum or magnesium and a is equal to the valence of the metal M", a compound having the formula TiX wherein X is chlorine or bromine and b is an integer from 2 to 4, inclusive, and elemental iodine, (4) a catalyst comprising an organometal compound having the formula R M', wherein R is an organo radical as defined above, M" is aluminum, gallium, indium, or thallium, and x is equal to the valence of the metal M', a titanium halide having the formula TiX wherein X is chlorine or bromine, and an inorganic halide having the formula M I wherein M is beryllium, zinc, cadmium, aluminum, gallium, indium, thallium, silicon, germanium, tin, lead, phosphorus, antimony, arsenic, and bismuth, and c is an integer from 2 to 5, inclusive, and (5) a catalyst comprising an organo compound having the formula R M'", wherein R, M' and x are as defined above, titanium tetraiodide, and an inorganic halide having the formula M X wherein M is aluminum, gallium, indium, thallium, germanium, tin, lead, phosphorus, antimony, arsenic or bismuth, X is chlorine or bromine, and d is an integer from 2 to 5, inclusive. The R radicals of the aforementioned formulas preferably contain up to and including 20 carbon atoms.

The following are examples of preferred catalyst sys terns which can be used to polymerize 1,3-butadiene to a cis 1,4-polybutadiene:

triisobutylaluminum and titanium tetraiodide triethylaluminum and titanium tetraiodide triisobutylaluminum, titanium tetrachloride and titanium tetraiodide triethylaluminum, titanium tetrachloride and titanium tetraiodide diethylzinc and titanium tetraiodide dibutylmercury and titanium tetraiodide triisobutylaluminum, titanium tetrachloride and iodine triethylaluminum, titanium tetrabromide and iodine n-amylsodium and titanium tetraiodide phenylsodium and titanium tetraiodide n-butylpotassium and titanium tetraiodide phenylpotassium and titanium tetraiodide n-amylsodium, titanium tetrachloride and titanium tetraiodide triphenylaluminum and titanium tetraiodide triphenylaluminum, titanium tetraiodide and titanium tetrachloride triphenylaluminum, titanium tetrachloride and iodine tri-alpha-naphthylaluminum, titanium tetrachloride and iodine tribenzylaluminum, titanium tetrabromide and iodine diphenylzinc and titanium tetraiodide di-2-tolylmercury and titanium tetraiodide tricyclohexylaluminum, titanium tetrachloride and titanium tetraiodide ethylcyclopentylzinc and titanium tetraiodide tri(3-isobutylcyclohexyl)aluminum and titanium tetraiodide tetraethyllead, titanium tetrachloride and titanium tetraiodide trimethylphenyllead, titanium tetrachloride and titanium tetraiodide diphenylmagnesium and titanium tetraiodide di-n-propylmagnesium, titanium tetrachloride and titanium tetraiodide triethylaluminum, titanium tetrachloride and phosphorus triiodide tri-n-dodecylaluminum, titanium tetrachloride and tin tetraiodide i triethylgallium, titanium tetrabromide and aluminum triiodide tri-n-butylaluminum, titanium tetrachloride and antimony triiodide tricyclopentylaluminum, titanium tetrachloride and silicon tetraiodide triphenylaluminum, titanium tetrachloride and gallium triiodide triisobutylaluminum, titanium tetraiodide and tin tetrachloride triisobutylaluminum, titanium tetraiodide and antimony trichloride triisobutylaluminum, titanium tetraiodide and aluminum trichloride triisobutylaluminum, titanium tetraiodide and tin tetrabromide triethyl-gallium, titanium tetraiodide and aluminum tribromide triethylal-uminum, titanium tetraiodide and arsenic trichloride tribenzylaluminum, titanium tetraiodide and germanium tetrachloride.

The polymerization process for preparing cis-polybutadiene is carried out in the presence of a hydrocarbon diluent which is not deleterious to the catalyst system. Examples of suitable diluents include aromatic, paraflinic, and cycloparafiinic hydrocarbons, it being understood that mixtures of these materials can also be used. Specific eX- amples of hydrocarbon diluents include benzene, toluene, n-butane, isobutane, n-pentane, isooctane, n-dodecane, cyclopentane, cyclohexane, methylcyclohexane, and the like. It is often preferred to employ aromatic hydrocarbons as the diluent.

The amount of the catalyst used in preparing the cispolybutadiene product can vary over a rather wide range. The amount of the organometal .used in the catalyst composition is usually in the range of 0.75 to 20 mols per mol of the halogen-containing component, i.e., a metal halide with or without a second metal halide or elemental iodine. The mol ratio actually used in a polymerization will depend upon the particular components employed in the catalyst system. However, a preferred mol ratio is generally from 1:1 to 12:1 of the organometal compound to the halogen-containing component. When using a catalyst reactor with a gas which is inert with respect to the polymerization reaction.

The present invention is also applicable to the process for polymerizing 1,3-butadiene with an organolithium compound and to the products obtained by this process. The polybutadienes prepared with an organolithium catalyst generally contain from 35 to 48 percent cis 1,4- addition, from 45 to 55 percent trans 1,4-addition, and from 6 to 10 percent 1,2-addition. The present invention is particularly applicable to low inherent viscosity polybutadienes prepared by this method. Such polymers generally have an inherent viscosity in the range of 0.75 to 3. While the low inherent viscosity polybutadienes possess outstanding properties, they have a tendency to cold flow when in the unvulcanized state.

Organolithium compounds suitable for use in the polymerization have the formula RLi wherein R is a hydrocarbon radical selected from the group consisting of aliphatic, cycloaliphatic and aromatic radicals and x is an integer from 1 to 4, inclusive. The R in the formula has a valence equal to the integer and preferably contains from 1 to 20, inclusive, carbon atoms, although higher molecular weight compounds can be utilized. In preparing the polybutadiene, it is often preferred to use an alkyllithium compound, such as n-butyllithiurn, as the catalyst. Examples of other suitable organolithium compounds include:

methyllithium isopropyllithium tert-octyllithium n-decyllithium phenyllithium naphthyllithium 4-butylphenyllithium p-tolyllithium 4-phenylbutyllithium cyclohexyllithium 4-butylcyclohexyllithium 4-cyclohexylbutyllithium dilithiomethane 1,4-dilithiobutane 1,10-dilithiodecane 1,20-dilithioeicosane 1,4-dilithiocyclohexane 1,4-dilithio-2-butene 1,8-dilithio-3 -decene 1,4-dilithiobenzene 1,5-dilithionaphthalene l,2-dilithio-l,2-diphenylethane 9,l-dilithio-9,l0-dihydroanthracene 1,2-dilithio-l,8-diphenyloctane 1,3,5 -trilithiopentane 1,5,15-trilithioeicosane 1,3,5 -trilithio cyclohexane 1,2,5-trilithionaphthalene 1,3,5 -trilithioanthracene 1,3,5 ,S-tetralithiodecane 1,5 l0,ZO-tetralithioeicosane 1,2,3 ,5-tetralithiocyclohexane l,2,3,5-tetralithio-4-hexylanthracene and the like.

The process used in preparing the organolithiumcatalyzed polybutadiene can be conducted at a temperature in the range of -l00 to 250 F., preferably at a temperature in the range of 0 to 180 F. The polymerization reaction can be carried out under autogenous pressures. It is usually desirable to operate at a pressure sufficient to maintain the reaction mixture in the liquid phase. The polymerization is conducted in the presence of a hydrocarbon diluent similar to that employed in the cispolybutadiene polymerization process as described hereinbefore. The actual pressure used in the process will depend upon the particular diluent employed and the temperature at which the polymerization is to be conducted.

A polybutadiene having a desired inherent viscosity can be readily prepared by varying the concentration of the organolithium compound. For example, with a comsystem and no other impurities present to destroy the organolithium compound, about 7 millimols of effective catalyst per 100 grams of monomer is generally required to give a polymer having an inherent viscosity of 0.75, and about 0.25 millimols of effective catalyst per 100 grams of monomer is generally required for the production of a polymer having an inherent viscosity of 3.0. It has been found that for practical operations approximately 0.3 mhm or more of catalyst is needed as a scavenger for the system.

Various materials are known to be detrimental to the organolithium catalyst and to the catalyst employed in preparing the cis-polybutadiene. These materials include carbon dioxide, oxygen and water. It is usually desirable, therefore, that the butadiene and diluent be freed of these materials as well as other materials which may tend to inactivate the catalyst. Furthermore, it is desirable to remove air and moisture from the reaction vessel in which the polymerization is to be conducted. Upon completion of the polymerization reaction in which cis-polybutadiene or the organolithium-catalyzed polybutadiene is prepared, the reaction mixture is then treated to inactivate the catalyst and recover the rubbery polymer. In accordance with one embodiment of the present invention, the catalyst is inactivated by adding to the reaction mixture sulfur dioxide or oxygen and in the case of the organolithium-catalyzed polybutadiene the R M compound as well. After this treatment of the reaction mixture, the polymer is then recovered by conventional methods, such as steam stripping, alcohol coagulation or the like. In accordance with another embodiment of the invention as hereinbefore described, the treating agents are added to the polymers in which no active polymerization catalyst is present. Accordingly, the polymerization reaction mixture is first treated to inactivate the catalyst and the rubbery polymer may also be recovered. A suitable method for accomplishing this result involves steam stripping the diluent from the polymer. In another suitable method, the catalyst-inactivating material, such as an alcohol, is added to the mixture so as to inactivate the catalyst and cause precipitation of the polymer. The polymer is then separated from the alcohol and diluent by any suitable means, such as decantation or filtration. Thereafter, the polymer is treated with the treating agent of this invention as described hercinbefore. It has been found to be advantageous to add an antioxidant, such as 4,4'-methylene-bis-(2,6-di-tert-butylphenol), to the polymer solution prior to recovery of the polymer.

A more comprehensive understanding of the invention may be obtained by referring to the following illustrative examples, which are not intended, however, to be unduly limitative of the invention.

pletely dry Example I Butadiene was polymerized in the presence of a catalyst system consisting of triisobutylaluminum, iodine, and titanium tetrachloride. This system produces a polymer containing about percent cis 1,4-addition. The following recipe was employed:

1 Millimols per parts monomer.

The procedure followed was to charge the toluene first, after which the reactor was purged with nitrogen. The butadiene was then added, followed by the triisobutylaluminum, iodine, and titanium tetrachloride in the order 9 named. Two series of runs were conducted in which the The data in Table I show that the addition of sulfur reaction mixtures were treated by injection of millimols dioxide to the polymerization reaction mixtures resulted the reactions. In one series of runs, the reaction mixtures 5 were at 41 F. when the sulfur dioxide was added. In the Example 11 other series, the reaction mixtures were at 122 F. A

control run was carried out in which the reaction was Variable initiator levels were employed for the Polym shortstopped at 41 with isepropyl aleohoi After erization of butadiene in the presence of triisobutyli bl periods f Contact of lf dioxide with the aluminum, 1od1ne, and titanium tetrachloride. Two runs reaction mixtures, the polymers (including the control) were made at each level. The reaction mixture of one of were eoagulated i h isopropyi l h and separated. Ah these runs was treated with sulfur dioxide while the other antioxidant was then incorporated into the wet polymers, run was Shortstopped Wlth P PY q T P aft hi h h products were dried dure followed was the same as that described 1n Example Samples of the polymer products were tested to measure T reclpes employffd the runs as Well as the c011 their tendency to cold flow The results f the tests are drtions for the sulfur dloxide treatment are shown below. shown below in Table I.

TABLE I POLYMERIZAIION RECIPES Cold Flow, mg./min. I A B 0 R Contact Time, 2 Reactions Terminated at- H011 1,3-butadicne, parts by weight 100 100 100 F R Toluene, parts by weight 860 860 860 Tnisobutylaluminum, mhm... 2. 4 2. 6 2. 8 Iodine, Ill 'll I I I I 0. 70 0. 76 O. 82 6.2 Titanium tetrachloride, mhm 0.40 0.43 0.47 67 "f5 Temperature, F 41 41 41 1 1 4 5 2' 4 Time, h )l1 S 1 18 18 18 2 9 0 Sulfur dioxide, mhm. 5 5 5 0 7 Temperature, F. 122 122 122 Time, hours 1. 5 1. 5 1. 5 1 Control, shortstopped with isopropyl alchohol. 2 Time between addition of S02 and addition of isopropyl alcohol to coagulate polymer.

C d flow wa measured by extrudme the rubber through a /i- Certain properties of the products obtamed were deteronfice at 3.5 psi. pressure and a temperature of 40 0. (122 F.). After allowing 10 minutes to reach steady state, the rate of extrusion was measm1ned- The results of these determmatlons are Shown ured and the values reported in milligrams per minute. b l i T bl 11 TABLE II Isopropyl S0 Isopropyl SO; Isopropyl S0 Alcohol Alcohol Alcohol Mooney (ML-4 at 212 F.) 27 35 20 27 17 24 Inherent Viscosity 1. 94 2.08 1. 1. 92 Gel, percent 3 0 0 0 0 old Flow, mgjminfi. 12. 7 0.33 28. 4 4. O0

1 ASTM D-297-551. One-tenth gram the cage was placed in ml. standing at room tern hours in toluene, the cage was w in the 2-ounce bottle. The same procedure was followed for determining the weight of swelled gel as was used for calibration of the cage. The weight of swelled gel was corrected by subtracting the cage calibration.

where E=extinction coefficient (liters-molscentimeters- L=extinction (log Io/I); t=path length (centimeters): and c=concentration (mcls double bond/liter). The extinction is determined at the 10.35 micron band and the extinction coefiicient used is 146 (litersmo1s- -centimeters The percent of the total unsaturation present as 1,2- (or vinyl) is calculated according to the above equation, using the 11.0 micron band and an extinction coefiicient of 209 (litersmols- -centimeters- The percent of the total unsaturation present as cis 1,4- is obtained by subtracting the trans 1,4- and 1.2- (vinyl) determined according to the above methods from the theoretical unsaturation assuming one double bond per each 04 unit in the polymer.

The data in Table II demonstrate that the tendency of cis-polybutadiene to cold flow can be greatly reduced by treating the polymerization reaction mixture with sulfur dioxide. The data also show that even though the polymers of this invention had higher Mooney values than the isopropyl alcohol-terminated polymers, there was no significant effect on inherent viscosity.

The foregoing SO -treated polymers, and a commercial cis-polybutadiene prepared with the same type of initiator system and shortstopped with rosin acid, were evaluated in a tread stock recipe. The commercial polymer had a raw Mooney value (ML-4 at 212 F.) of 46.5, an inherent viscosity of 2.54 and a cold flow of 3.6- rug/min. The following compounding recipe was used:

Pl1ysica1 mixture containing 65 percent of a complex diarylamine-ketone reaction product and 35 percent of N,N- diphenyl-p-phenylenediamine.

- Disproportionated pale rosin Aromatic oil.

4 N-oxydiethylene-fl-benzothiazyl sulfenamide.

stable to heat and light.

Extrusion ratings and compounded Mooney values were obtained on each of the compounded stocks. The stocks were cured for 30 minutes at 307 F. and physical properties were determined. The results of these determinations are shown below in Table III.

TABLE III Reaction Mixture Treated With- S02 S S01 Rosin Acid Mooney (ML-1% at 212 F.) 34. 2 26. 23.0 43. 5 Extrusion rating (Garvey die 2 12- 12 12 7- Physical Properties, Cured 30 Minutes at 307 F;

1000*, moles/cc. 1.90 1. 75 1.77 1. 05 300% Modulus, p.s.i. 1,180 080 1,210 1,200 Tensile, p.s.i. 2, 240 2, 260 2, 000 2, 365 Elongation, percent 440 475 450 455 Shore A hardness 61. 0 60.0 59.0 61. 5 Heat Build-up, A T, 1* 40.9 49. 3 47. 9 44.6 Oven Aged 24 Hours at 12 300% Modulus, p. 1,325 1,270 1, 360 1,270 '1enslle,p.s.i. 1,710 1,510 1, 085 1,760 Elongation, pcrce 235 220 230 245 Heat Build-up, A 35.1 37. 5 34. 8 36. 5

chains per unit volume of rubber. The higher the number, the more the rubber is crosslinked (vulcanized).

4 ASTM D41251T. Scott Tensile Machine L-6. Tests made at 80 13.

5 ASTM D676-55T. Shore Duremeter, Type A.

5 AS'IM D62352T. Method A, Goodrich Flexorneter, 143 lbs/sq. in. load, 0.175 inch stroke. Test specimen is a right circular cylinder, 0.7 inc in diameter and 1 inch high.

The data in Table III show that the polymers of this invention had lower Mooney values than the commercial polymer but the physical properties of the vulcanizates were very similar.

12 Example 111 A series of runs was conducted in which 1,3-butadieue was polymerized with a catalyst consisting of diethylzinc and titanium tetraiodide. The polybutadiene products obtained with this catalyst system contain at least percent cis 1,4-addition. The recipe employed in the runs was as follows:

Three runs were made. Immediately following polymerization, the runs were shortstopped with sulfur dioxide, oxygen and isopropyl alcohol, the latter being used as a control. After addition of the treating agents, the temperature was held at 122 F. for one hour while the mixtures were agitated. The polymers were recovered as described in Example I and cold flow and Mooney values were determined. The results obtained are shown in Table IV.

TABLE IV Shortstopping Cold MM 1 Inh. Gel. Run Agent Flow, at 212 F. Vise. Per- Mg/min. cent 8 mhm. S02 0.2 78 2 14 22 8 mhm. 0 (as air) 1. 3 38 2 22 0 Control 3. 9 24 1. 0

1 See appropriate footnotes to Tables I and II.

Example IV A polybutadiene was prepared by polymerizing 1,3- butadiene with n-butyllithium. The following recipe was employed:

RECIPE Cyclohexane, parts by weight 950 1,3-butadiene, parts by weight n-butyllithium, rnhm. 1.2 Temperature, F. 122 Time, hours 16 1 Obtained as a normal heptane solution; diluted with cyclohexane.

- \Iillimols per 100 parts monomer.

Cyclohexane was charged first to the reactor. The reactor was then purged with nitrogen, and butyllithium was added. Conversion was substantially quantitative in 16 hours.

Various portions of the unquenched polymer solution were treated in different ways. One portion was reserved as a control, one was treated with sulfur dioxide, another with oxygen added as air, and a combination of triisobutylaluminum with either sulfur dioxide or oxygen was used to treat two other portions. Sulfur dioxide and oxygen (as air) were added in the gaseous form while triisobutylaluminurn was introduced as a solution in toluene. Treatment was carried out at 122 F. for one hour while the mixtures were agitated. One part by weight per 100 parts rubber of the antioxidant 2,2'-methylenebis(4-methyl-6-tert-butylphenol) was added to each mixture after which the polymers were coagulated in isopropyl alcohol, separated, and dried in a vacuum oven at 60 C. The results of cold flow, inherent viscosity, gel, and Mooney determinations are shown in Table V.

v TABLE v Run Gel, ML-4 at 1 No. Treatment F Per- 212 F.

cent R 1 None. 2 2.11 27.0 2 2 mhm. triisobutylalnminum plus 8 mhm. S02 4. 0 2. 18 O 36. 3 2 mhm. triisobutylaluminum plus 8 mhm. 0 (as air) 4. 7 2.09 0 37. 5 4 l6 mhrn. S02 12 3 2.01 0

5 16 mhrn. oi (as air) 261 e .02

1 See appropriate footnotes to Tables I and II. 2 Not detected.

These data show that a significant reduction in cold flow RECIPE is achieved by treating the polymer solution with a com- V g bination of triisobutylaluminum with either sulfur dioxide 1,3- utad1 ne, parts by Weight 100 or oxygen. Sulfur dioxide alone has substantially no effect Toluene, parts by weight 860 on cold flow while oxygen alone increases cold flow. Triisobutylaluminum, rnhm. 2.8 Example V 20 Io ine, mhm. 0.82 Titanium tetrachloride, rnhrn. 0.47 The following recipe was employed for the polymerlza- Tfim o perature, F. 41 tlon of butadlene:

Time, hours 20 RECIPE Conversion, percent approx 90 Cyclohexane, parts by weight 930 1,3 -butadiene, parts by weight 100 1 Millimols P 100 Darts 111011011161- n-Butyllithium, mh'rn. 1.76 Temperature, 0 F 122 Toluene was charged first after which the reactor was Ti hours 14 purged with nitrogen. Butadiene was then added, followed 1A5 in Example L by the triisobutylaluminum, iodine, and titanium tetrachloride in the order named. The reaction was shortg f gggg f g gg ig f igfj gg gjg if if??? stopped by the addition 0t 0.6 milliliter of water per 100 quenched polymer solution was reserved as a control, one pans monomer after Whlch anhydrous calcmm Sulfate was treated with triisobutylaluminu-m, and another with Was adfled to k up excess Water Varlous portions of the polymer solution were treated was carried out at 122 F. for 1.5 hours. An antioxidant in diifel'ent y one Portion Y reserved control, was added and the polymers we e o er d as i Example sulfur dioxide was introduced lnto another portion, and I. The results of the runs are shown below in Table VI. a combination of sulfur dioxide with trnsobutylalumlnum TABLE VI Run Cold Inh. (tel, ML-4 at N 0. Treatment Flow, Vise. Per- 212 F.

MgJmin. cent a 1 None. 63 1. 47 0 5.8 4 mhm. tliisobutylaluminum plus 6 mhm. S01 20 1. 57 8 g 3 4 mhm. triisobutylalumin 76 1.40 K

1 See appropirate footnotes to Tables I and II.

The control polymer in these runs had a very low was used to treat another portion. Sulfur dioxide was Mooney value and a high cold flow while a substantial added as a gas after the organometal was added as a reduction was achieved when sulfur dioxide was used in solution in toluene. Treatment was carried out at 122 F. conjunction with this reagent. 7 for one hour while the mixtures were agitated. One part Emmple W by weight per 100 parts rubber of the antioxidant 2,2- methylene-bis(4-methyl-6-tert-butylphenol) was added to A run was conducted in which butadiene was polyrneach mixture after which the polymers were coagulated erized with a catalyst consisting of triisobutylaluminum, in isopropyl alcohol, separated, and dried in a vacuum titanium tetrachloride and iodine. The following recipe oven at 60 C. The results of cold flow, inherent viscosity, was used: gel, and Mooney determinations are shown in Table VH.

TABLE VH Run Cold InhJ Gel, ML-4 at 1 No. Treatment Flow, Vise. Per- 212 F.

cent

15 These data show that the cold flow was reduced with a combination of triisobutylaluminum and sulfur dioxide. However, sulfur dioxide when used alone was ineffective in reducing cold flow.

Example VII TABLE VIII Cold flow, mg./min. 0.65 Inherent viscosity 1 2.10 Gel, percent 1 1 See appropriate footnotes to Tables I and II.

A comparison of this run with the control in the preceding example shows that a very substantial reduction in cold flow was achieved by treating the polymer with triisobutylaluminum and air.

Example VIII Various 30-gram portions of a 37-Mooney polybutadiene prepared in the presence of n-butyllithium were dissolved in 200 milliliters of toluene. The resulting solutions treated in different ways as follows: (1) triisobutylaluminum (TBA) +50 (2) triisobutylaluminum-l-oxygen, (3) triisobutylaluminum, (4) oxygen, and (5) S Sulfur dioxide and oxygen (as air) were added in the gaseous form while triisobutylaluminum was introduced as a solution in toluene. Treatment was carried out at 122 F. for 30 minutes while the mixtures were agitated. An antioxidant was added as in Example VI and the mixtures were allowed to stand overnight at room temperature after which the polymers were coagulated in isopropyl alcohol, separated, and dried in a vacuum oven at 60 C. The results of cold flow and Mooney value determinations are shown in Table IX.

TABLE 1X Run Cold ML-4 at 1 No. Treatment Flow, 1 212 F Mg./min.

1. TBA (7 mhr.) 2 plus S02 (16 mhr.) 0.8 48.2 2. TBA (7 mhng plus 03 (16 mhr.) as air. 0.4 58.0 3... TBA (7 min. 4.1 41.0 4".-- O (16 mhr.) as air 6.7 35.0 5 S01 (16 ml\r.). 7.8 37.0 6 8.5 35.0

1 See appropriate footnotes to Tables I and II. 9 Millimols per 100 grams of rubber.

These data demonstrate the elfectiveness of triisobutylaluminum used in combination with sulfur dioxide or oxygen in reducing the cold flow of polybutadiene prepared in the presence of an organolithium initiator. However, none of these materials when used alone was effective in reducing cold flow.

As will be evident to those skilled in the art, many variations and modifications of the invention can be practiced in view of the foregoing disclosure. Such variations and modifications are believed to come within the spirit and scope of the invention.

1 claim:

1. In a process wherein a polymerization reaction mixture is formed by polymerizing 1,3-butadiene with an organolithium catalyst, the improvement which comprises adding to said reaction mixture (1) oxygen and (2) an organometal having the formula R M, wherein R is selected from the group consisting of aliphatic, cycloaliphatic and aromatic radicals, M is a metal selected from the group consisting of sodium, potassium, beryllium, magnesium, zinc, cadmium, mercury, aluminum, gallium, indium, thallium and lead, and n is an integer equal to the valence of the metal M', and recovering a polybutadiene product having a reduced tendency to cold flow in the unvulcanized state.

2. In a process wherein a polymerization mixture is formed by polymerizing 1,3-butadiene in the presence of a hydrocarbon diluent with an organolithium catalyst, said polymerization occurring at a temperature in the range of l00 to 250 F. and at a pressure sufficient to maintain said reaction mixture substantially in the liquid state, the improvement which comprises adding to the unquenched reaction mixture (1) oxygen and (2) an organometal having the formula R M, wherein R is selected from the group consisting of aliphatic, cycloaliphatic and aromatic radicals, M is a metal selected from the group consisting of sodium, potassium, beryllium, magnesium, zinc, cadmium, mercury, aluminum, gallium, indium, thallium and lead, and n is an integer equal to the valence of the metal M; maintaining said added oxygen and organometal in contact with said polymerization mixture at a temperature in the range of -l00 to 250 F. and for a period of time in the range of 5 minutes to 50 hours; and recovering a polybutadiene product having a reduced tendency to cold flow.

3. The process according to claim 1 in which said catalyst is an alkyllithium compound and oxygen and a trialkylaluminum are added to said reaction mixture.

4. The process of claim 2 wherein said organolithium catalyst is n-butyllithium and said organometal compound is triisobutylaluminum.

5. A process for reducing the tendency of a polybutadiene to cold flow when in the unvulcanized state, said polybutadiene having been prepared by polymerizing 1,3- butadiene in the presence of a catalyst system selected from the group consisting of (1) an iodine-containing catalyst including an organometal and a titanium halide, and (2) an organolithium catalyst, said process comprising the steps of blending said polybutadiene with (l) oxygen and (2) an organometal having the formula R M, wherein R is selected from the group consisting of aliphatic, cycloaliphatic and aromatic radicals, M is a metal selected from the group consisting of sodium, potassium, beryllium, magnesium, zinc, cadmium, mercury, aluminum, gallium, indium, thallium and lead, and n is an integer equal to the valence of the metal M, the amount of said oxygen used being in the range of l to 60 millimols per grams of polybutadiene, the amount of said R M compound being in the range of 0.5 to 25 millimols per 100 grams of polybutadiene, and the mol ratio of said oxygen to said R M compound being in the range of 1.1 to 25, said blending occurring at a temperature in the range of 50 to 250 F. for a period of from 5 minutes to 50 hours; and recovering a polybutadiene having a reduced tendency to cold flow.

6. A process for reducing the tendency of a polybutadiene to cold flow when in the unvulcanized state, said polybutadiene having been prepared by polymerizing 1,3- butadiene in the presence of a catalyst system selected from the group consisting of (1) an iodine-containing catalyst including an organometal and a titanium halide, and (2) an organolithium catalyst, said process comprising the steps of blending said polybutadiene with (a) oxygen and (b) an organoaluminum compound having the formula R Al wherein R is selected from the group consisting of aliphatic, cycloaliphatic and aromatic radicals, the amount of said oxygen used being in the range of l-60 millimoles per 100 grams of polybutadiene, the amount of said organoaluminum compound being in the range of 0.5 to 25 millimoles per 100 grams of polybutadiene, and the mol ratio of said oxygen to said organoaluminum compound being in the range of 1.1 to 25, said blending occurring at a temperature in the range of 50-250" F. for a period of from 5 minutes to 50 hours; and recovering a polybutadiene having a reduced tendency to cold flow.

7. The process of claim *6 wherein said organoaluminum compound is a trialkylaluminum compound.

8. The process of claim 7 wherein said polybutadiene is a cis-polybutadiene containing at least 85 percent cis-1,4 addition.

9. The process of claim 7 wherein said organolithium catalyst is n-butyllithium.

18 References Cited UNITED STATES PATENTS 2,979,488 4/ 1961 Carpenter 2.6094.3 3,036,056 5/1962 Rion 26094.3 3,094,514 6/1963 Tucker 26094.3 3,182,052 5/1965 Naylor 26094.3 3,245,978 4/1966 Gregorian et a1 26094.9

10 JAMES A. SEIDLECK, Primary Examiner. 

1. IN A PROCESS WHEREIN A POLYMERIZATION REACTION MIXTURE IS FORMED BY POLYMERIZING 1,3-BUTADIENE WITH AN ORGANOLITHIUM CATALYST, THE IMPROVEMENT WHICH COMPRISES ADDING TO SAID REACTION MIXTURE (1) OXYGEN AND (2) AN ORGANOMETAL HAVING THE FORMULA RNM, WHEREIN R IS SELECTED FROM THE GROUP CONSISTING OF ALIPHATIC, CYCLOALIPHATIC AND AROMATIC RADICALS, M IS A METAL SELECTED FROM THE GROUP CONSISTING OF SODIUM, POTASSIUM, BERYLLIUM, MAGNESIUM, ZINC, CADMIUM, MERCURY, ALUMINUM, GALLIUM, INDIUM, THALLIUM AND LEAD, AND N IS AN INTEGER EQUAL TO THE VALENCE OF THE METAL M; AND RECOVERING A POLYBUTADIENE PRODUCT HAVING A REDUCED TENDENCY TO COLD FLOW IN THE UNVALCANIZED STATE. 